A planar rotating interferometric fiber optic gyro is designed to produce an accurate phase difference, DeltaPhi(t), between a counter clock-wise light loop and a clock-wise light loop, for a gyro rotation rate OMEGA. However, a planar rotating interferometric fiber optic gyro can produce an erroneous phase difference, DeltaPhi′(t), due to temperature, mechanical effects or other environmental influences. DeltaPhi′(t) is a measured phase difference that is not the accurate phase difference, DeltaPhi(t).
DeltaPhi′(t) is a measured phase difference over time between two light loops in the rotating interferometric fiber optic gyro. DeltaPhi′(t) occurs when a fiber optic gyro is experiencing an applied rotational velocity OMEGA.
A variation between a measured phase difference, DeltaPhi′(t), and an accurate phase difference, DeltaPhi(t), is gyro phase drift. Such gyro phase drift can be due to a temperature variation in the rotating interferometric fiber optic gyro, or due to a mechanical variation in the rotating interferometric fiber optic gyro. The amount of gyro phase drift can slowly change with time.
Gyro phase drift is evidenced as a difference value DeltaPhi(t)−DeltaPhi′(t) or DeltaPhi′(t)−DeltaPhi(t) for an applied planar rotational velocity, OMEGA, of an interferometric fiber optic gyro.
An erroneous phase difference, DeltaPhi′(t), will cause a planar rotational velocity measurement, OMEGA', to be made by the interferometric fiber optic gyro.
Laser light, in each of the two light beams, has the same phase Phi(t) as the laser light enters the single optical fiber cable. The phase difference between the two exiting counterrotating light beams is detected in the interference pattern. Ideally, an accurate phase difference, DeltaPhi(t)=(Phi1(t)−Phi2(t)), or Delta Phi(t)=(Phi2(t)−Phi1(t)), should be produced due to a counterclockwise or clockwise planar angular rotational velocity of the fiber optic gyro.
Gyro phase drift changes with time, and tends to be slowly continuous, in a mathematical sense. The present invention uses the continuity of slow gyro phase drift changes to eliminate the overall effect of gyro phase drift.